1. Field of the Invention
This invention relates to tools and methods for orthopedic surgery generally and more specifically to bone screws and cables for fixation of fractured bones.
2. Description of the Related Art
In various medical procedures wires or cables are used to join fractured bones. Typically, metal alloy cables are preferred; but synthetic polymer cables are sometimes employed. For example, U.S. Pat. No. 6,093,190 to Mattchen describes a method of using elastomeric cables to stabilize and compress fractured bones, by spanning a network of tensioned cables across a fracture. Such a network can provide stable fixation of a fracture in both linear and torsional directions. The method disclosed also provides a tensile preload across the fracture, tending to compress the fracture and maintain fixation despite tensile and shear loads (such as those resulting from movement, weight bearing and bone remodeling).
Many polymeric, elastic cable constructions have desirable engineering properties and are known to be biocompatible. However, manipulation and fixation of some polymer cables is inconvenient with traditional methods and fasteners. Metal wires and cables are easily joined at their ends using surgical knots or known surgical fasteners, including screws. Various known cable tensioner devices may be employed to attain desired tensioning in loops formed by tied or crimped wires and cables. On the other hand, certain elastic, polymer cables are not so easily fixed. Cables engineered for extreme elongation under tension tend to change diameter in response to tension, and tend to escape from conventional gripping devices. The problem is further exacerbated by the incidental fact that many polymer cables (or coatings) have a low coefficient of friction, and are thus prone to slip. Gripping such a cable with extremely localized, high pressure is not an adequate solution, because localized high compression can lead to failure by cutting the cable.
An improved method and device is desirable for securely anchoring high strength, polymeric cables to a bony structure.